Method of making a reagent test device containing hydrophobic barriers

ABSTRACT

Reagent test devices are prepared in which reagent carrier matrices are separated from each other by hydrophobic barrier pads of identical height to the reagent carrier matrices such that liquid present in a reagent matrix material is retained therein and prevented from running over into another reagent matrix area present on the same test device.

This is a division of application Ser. No. 771,061, filed Aug. 30, 1985now U.S. Pat. No. 4,618,475.

FIELD OF THE INVENTION

The present invention relates to a reagent test device comprisingreagent pads separated by a hydrophobic barrier pad attached to asubstrate and, more particularly, to such test devices and a method offorming such test devices such that the reagent pads and the barrierpads have the same thickness. The alternating reagent pads and barrierpads mounted on a substrate prevent or minimize cross-contamination ofreagents during use and also minimize damage to the reagent pads.

BACKGROUND OF THE INVENTION

The art of analytical chemistry has been greatly advanced sincebiochemistry began emerging as a primary scientific frontier, requiringincreasingly sophisticated analytical methods and tools to solveproblems. Likewise the medical profession has lent impetus to the growthof analytical chemistry, with its desiderata of both high precision andspeed in obtaining results.

To satisfy the needs of the medical profession as well as otherexpanding technologies, such as the brewing industry, chemicalmanufacturing, etc., a myriad of analytical procedures, compositions andapparatus have evolved, including the so-called "dip-and-read" typereagent test device. Reagent test devices enjoy wide use in manyanalytical applications, especially in the chemical analysis ofbiological fluids, because of their relatively low cost, ease ofusability, and speed in obtaining results. In medicine, for example,numerous physiological functions can be monitored merely by dipping areagent strip test device into a sample of body fluid, such as urine orblood, and observing a detectable response, such as a change in color ora change in the amount of light reflected from or absorbed by the testdevice.

Many of the "dip-and-read" test devices for detecting body fluidcomponents are capable of making quantitative or at leastsemiquantitative measurements. Thus, by measuring the response after apredetermined time, an analyst can obtain not only a positive indicationof the presence of a particular constituent in a test sample, but alsoan estimate of how much of the constituent is present. Such test devicesprovide the physician with a facile diagnostic tool as well as theability to gage the extent of disease or of bodily malfunction.

Illustrative of such test devices currently in use are productsavailable from the Ames Division of Miles Laboratories, Inc. under thetrademarks CLINISTIX, MULTISTIX, KETOSTIX, N-MULTISTIX, DIASTIX,DEXTROSTIX, and others. Test devices such as these usually comprise oneor more carrier matrices, such as absorbent paper, having incorporatedtherein a particular reagent or reactant system which manifests adetectable response, e.g., a color change, in the presence of a specifictest sample component or constituent. Depending on the reactant systemincorporated with a particular matrix, these test devices can detect thepresence of glucose, ketone bodies, bilirubin, urobilinogen, occultblood, nitrite, and other substances. A specific change in the intensityof color observed within a specific time range after contacting the testdevice with a sample is indicative of the presence of a particularconstituent and/or its concentration in the sample. Some of these testdevices and their reagent systems are set forth in U.S. Pat. Nos.3,123,443; 3,212,855 and 3,814,668.

Thus, it is customary for reagent test devices to contain more than onereagent bearing carrier matrix, in which each reagent bearing carriermatrix is capable of detecting a particular constituent in a liquidsample. For example, a reagent test device could contain a reagentbearing carrier matrix responsive to glucose in urine and another matrixresponsive to ketones, such as acetoacetate, which is spaced from, butadjacent to, the glucose responsive matrix. Such a product is marketedby the Ames Division of Miles Laboratories, Inc. under the trademarkKETO-DIASTIX. Another reagent test device marketed by the Ames Divisionof Miles Laboratories, Inc., N-MULTISTIX, contains eight adjacentreagent incorporated matrices providing analytical measurement of pH,protein, glucose, ketones, bilirubin, occult blood, nitrite, andurobilinogen.

Despite the obvious, time-proven advantages of such multiple reagenttest devices as these, misuse can result in misinformation. Thesemultiple analysis tools comprise complex chemical and catalytic systems,each reagent matrix containing an unique reactive system, responsive toits particular analyte. Thus, it is possible, if the reagent test deviceis misused, for chemicals to be transported by the liquid sample beinganalyzed from one carrier matrix on the reagent test device to another.Should this happen it is possible for reagents from one carrier matrixto interfere with those of the other so contacted causing unreliableresults. Although it is common in the reagent test device industry toprovide detailed instructions on how this problem can be minimized,i.e., directions for properly manipulating the reagent test devices byblotting excess fluid, nevertheless ignorance or disregard of theseinstructions could permit reagents from one matrix to run over onto anadjacent one. Cross-contamination can result in false results. It is theprevention of this "runover" problem that the present invention isprimarily directed.

The elimination of runover has been long sought after and the presentdiscovery, which is the cumulation of an extensive research effort,provides a very effective solution to this problem. The presentinvention also minimizes damage caused by abrasion of the reagent padsduring storage and use.

LITERATURE DISCUSSION

The patent literature is replete with accounts of myriad attempts atcurtailing runover, the great bulk of the emphasis being directed to twobasic concepts: the absorbance of runover liquid by bibulous layersplaced beneath the reagent-bearing layers of reagent test devices; andthe creation of hydrophobic barriers between the spaced matrices. Theformer has met with moderate success, whereas the latter approach hasnot.

Of the multilayer type reagent test devices, U.S. Pat. No. 4,160,008describes a test device in which the carrier matrices containing reagentformulations are provided with absorbent underlayers which are separatedtherefrom by sample impervious barrier layers. Each matrix thus formsthe upper layer of a laminate composite in which the barrier layer isdisposed between the matrix and the absorbent base layer, the compositebeing fixed to a suitable support such as a plastic substrate. When thetest device is dipped into the liquid sample the portion of sample whichwould otherwise runover from one matrix to another is largely absorbedinto the underlayer of the latter through the exposed sides, the barrierlayers of the composite preventing the absorbed runover from reachingthe upper reagent layers.

U.S. Pat. No. 4,301,115 discloses and claims a test device comprising abase support member coated with a hydrophobic barrier layer to which aplurality of spaced apart reagent matrices are affixed. This approachvirtually eliminates cross-contamination between adjacent reagent areasof multiple reagent test devices, but requires an extra step of applyinghydrophobic material to the base support member of the reagent testdevice.

With respect to the development and use of barriers and/or barriermaterials between reagent matrices, the patent literature is repletewith teachings, which in theory, at least, would seem to overcome therunover problem.

U.S. Pat. No. 3,418,083 discloses an indicator-impregnated absorbentcarrier matrix treated with wax, oil or similar "hydrophobic" agents. Itis stated that when a sample of blood is placed on the resulting reagenttest device, only colorless liquid components permeate it, theproteinaceous, colored blood components remain on the surface where theycan be removed. Thus, it is taught that the liquid portion bearing theanalysate permeates the reagent matrix pad and color interference isprecluded.

Still another patent, U.S. Pat. No. 3,001,915, describes an absorbentpaper reagent test device having spaced reagent-impregnated test areasfor more than one sample component, each such area being separated fromthe other reagent-impregnated test area by a nonabsorbent barrierportion. The barrier is provided by impregnation of the paper strip withmaterials such as polystyrene, rosin, paraffin and various celluloseesters. The reagent strip is prepared, according to the reference, byimpregnating a portion of the paper strip with a glucose sensitivereagent system. When dry, a solution of one or more of the barriermaterials is applied to the paper adjacent a glucose sensitive portion.After further drying a protein sensitive reagent system is applied andthe process is repeated with alternate applications of reagent andbarrier solutions with drying steps inbetween.

Yet an earlier patent, U.S. Pat. No. 2,129,754, describes theimpregnation of filter paper with paraffin wax whereby specific areasare left unimpregnated and these areas are treated with indicatorsystems for a particular analyte.

In U.S. Pat. No. 3,006,735 the concept of barrier material impregnatedbetween reagent areas of a reagent test device is carried one stepfurther by providing successive reagent areas responsive to differentdegrees of water hardness. Water repellent material, such as oils,waxes, silicones, and printer's varnish, is impregnated between thesereagent test areas. Like the proceeding two patents this citation isrestricted to paper or like bibulous material wherein reagent andbarrier material alike are impregnated sequentially along the testdevice.

Despite lip service given by literature accounts to the elimination ofrunover, the fact remains that the problem continues to exist. Theapproaches disclosed in U.S. Pat. Nos. 4,160,008 and 4,301,115 have comethe closest to eliminating the runover problem.

Prior attempts using wax, oils, silicones, and the like materials, havenot curtailed runover to a clinically significant extent; and whatmodest advances have been made are more than offset by serious drawbacksinherent to such attempts. For example, applying hydrophobic materialonly at reagent area interstices embodies technical problems, especiallywhen compared with the current techniques for manufacturing dip-and-readreagent test devices. Besides the obvious extra steps required byinterstitial application, there is the danger of some of the hydrophobicmaterial overlapping the reagent area thereby interfering with theparamount purpose of the reagent test device. Moreover, none of thesubstances taught by the prior art provides a suitable surface foradhesion.

Even if the above shortcomings were not prohibitive enough, the priorart hydrophobic substrates lack a degree of hydrophobicity required toprevent runover. They do not provide a sufficient contact angle toachieve the required hydrophobicity, nor do they provide a suitablesurface for binding either the absorbent matrices or the reagentsthemselves, where they are coated directly on the substrate surface.

Unlike the prior efforts to establish a "barrier" between reagent areasof a test strip, the present invention does not attempt to create thebarrier area by impregnating or coating a portion of the test strip. Infact, the barrier material of the present invention can be made from anentirely different type of material from that used to form the reagentpad. In any event, the construction of the test devices according to theinvention permits the barrier material to be made entirely fromhydrophobic material or be thoroughly saturated with hydrophobicingredients prior to the formation of the test device to prevent anypossible path through the barrier material from one reagent pad toanother.

The present invention virtually eliminates cross-contamination betweenadjacent reagent areas of multiple reagent test device matrices. Theresults are truly incontrovertible and the success achieved in solvingthis problem represents an improvement over the use of a hydrophobicbarrier layer, as described in U.S. Pat. No. 4,301,115. Moreover, thepresent invention has the advantages resulting in an excellentappearance of the final product in that the surface of the reagent testdevice is flat with no shadows between the reagent pads; the reagenttest device is "stiffer" making the reagent test device easier to useand more accurate by reducing variations in instrument readings due toheight variations; and the presence of the barrier pads of the sameheight as the reagent pads substantially reduces abrasion betweenreagent areas during transportation as well as materially reducingdamage to the reagent pad areas during use.

SUMMARY OF THE INVENTION

An object of the present invention is to substantially eliminate runoverproblems by inserting a hydrophobic barrier between each reagent pad ona reagent test device.

Another object of the present invention is to eliminate abrasion betweenreagent test devices during transportation and minimize damage to thereagent pads during use by inserting a barrier area between the reagentpads which is of identical height to the reagent pads.

Still another object of the present invention is to provide a reagenttest device with barrier materials inserted between reagent pads inwhich the barrier materials are constructed from different material fromthat of the reagent pads such that the barrier materials effectivelyeliminate runover between the reagent pads.

In accordance with the present invention, a reagent test devicecontaining multiple reagent pads is formed with separate hydrophobicbarrier pads separating each reagent pad and the barrier pads aremaintained identical in height to the reagent pads so as to protect thereagent pads from abrasion or other damage during storage and use. Thetest devices of the present invention can be formed according to apreferred procedure by separately laminating hydrophobic reagent padsand hydrophobic barrier pads to a substrate while the substrate ismaintained in a convex position such that when released from thecurvature there is no gap or space between the reagent pads and thebarrier pads.

DESCRIPTION OF THE DRAWINGS

Other and further objects, advantages and features of the invention willbe apparent to those skilled in the art from the following detaileddescription thereof, taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic cross-sectional view of a test device inaccordance with the present invention; and

FIG. 2 is a schematic view of a test device in accordance with thepresent invention showing a preferred method of applying the reagentpads and barrier pads to the substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention reagent test devices areprepared having alternating reagent pads and barrier pads attached to asubstrate in such fashion that there is no space between the pads andall of the pads are of the same height.

Referring to the drawings, FIG. 1 illustrates a test device 10 preparedin accordance with the present invention. Reagent test device 10 iscomposed of a substrate 12 containing three reagent pads 13, 14 and 15separated by barrier pads 17 and 18. In addition, barrier pad 19 isshown on the end of test device 10 and another barrier pad 20 is shownon the opposite side of reagent pad 15 from barrier pad 18. The reagentpads 13-15 and the barrier pads 17-20 are separately bound to substrate12 by means of a glue or adhesive 22-28 which connects the respectivepads to substrate 12.

It will be observed that the resulting test device 10 provides a stifferor more rigid test device than the conventional test device which doesnot have the barrier pads between the reagent pads. This featurefacilitates the presentation to instruments for determining reflectancevalues and tends to improve the overall appearance and accuracy of thetest device. Since the upper surface of the reagent area is flat thereexists no clear demarcation line at the end of the reagent pads and noshadow exists. Moreover, the flat surface is very advantageous in thatit minimizes abrasion between reagent pads during storage in a bottle orcontainer, during transportation and in use. Conventional test devices,with reagent pads extending above a substrate surface, tend to exposethe reagent pads to abrasion during storage and transit and subject thereagent pads to pressure when the exposed edges of the pad are caught onother pads or instruments used in the analysis procedure. Even if areagent pad is not completely torn off a conventional reagent testdevice, it is important to minimize any contact which deforms or changesthe surface or edges of a reagent pad since a slight deformation of thereagent pad surface can create substantial distortion in instrumentalreflectance readings.

The barrier pads which separate reagent pads tend to be much moreeffective than prior art "barriers" placed between reagent test padssince the procedure for forming and applying the barrier pads is suchthat it permits all of the material used in a barrier pad to behydrophobic. Preferably, the barrier pad is formed from a material whichis completely different from that of the reagent pad. Thus, problemsassociated with attempts to employ the same material for both theimpregnated reagent pad and for the impregnated barrier area areavoided. These problems include the problem of attempting to obtainsubstantial impregnation of hydrophobic barrier material and limit thatimpregnation to the barrier pad area such that there is no interferencewith the impregnated reagents. In the past it was often necessary to usehydrophilic material as the barrier material in order to obtain anyimpregnation.

The invention also makes it much easier to print a reagent test devicewith symbols or other designations and with "background color" on thebarrier pads adjacent to the reagent pads, which symbols and colorfacilitate the accurate use of the resulting reagent test device.

FIG. 2 illustrates a preferred method of forming the reagent test deviceof FIG. 1. Since it is important to maintain the reagent pads andbarrier pads adjacent to each other with no gaps in between and sincethe reagent pads and barrier pads must be applied separately, eithersequentially or concurrently, bending the substrate 12 slightly to forma convex surface facilitates applying the reagent pads and the barrierpads adjacent to each other such that when the flexible substrate 12 isreleased from its convex position the upper edges of the reagent padsand barrier pads come together leaving no space between them.

The substrate 12 can be formed from any suitable material includingpolystyrene, polyvinylchloride, polyethylene, polycarbonate, etc.Preferably the substrate 12 is flexible to facilitate manufacture inaccordance with the procedure described above. Typically, the testdevice 10 will contain an elongated substrate such that one end 30 ofsubstrate 12 can be used as a handle when the test device is dipped orcontacted with test fluid being analyzed. The preferred material isTrycite, polystyrene, made by Dow Chemical Company.

The glue or adhesive material employed to bind the reagent pads and thebarrier pads to substrate 12 can be any suitable material which iscapable of bonding the pads to the substrate and readily adhering thedifferent materials together. Double backed adhesive tape known aDouble-Stick, available from the 3M Company, is preferred.

Reagent pads 13, 14 and 15 can be formed from any suitable material.U.S. Pat. No. 3,846,247 teaches the use of felt, porous ceramic materialand woven or matted glass fibers. Additionally, U.S. Pat. No. 3,552,928teaches the use of wood, cloth, sponge material and argillaceoussubstances. The use of synthetic resin fleeces in glass fiber felts ascarrier matrix material is suggested in British Pat. No. 1,369,139.Another British Pat. No, 1,349,623, proposes the use of light permeablemeshwork of thin filaments as a cover for an underlying paper matrix.Polyimide fibers are taught in French Pat. No. 2,170,397.Notwithstanding these suggestions, however, the material predominantlyused in the art as carrier matrix for the reagent pads and those whichare especially useful in the present invention are bibulous paper, suchas filter paper, and porous hydrophilic film.

The reagent pad is normally impregnated with reagent material prior tobonding of the reagent pad to the substrate 12 using the adhesivematerial. Obviously, the reagents employed to impregnate reagent pads13, 14 and 15 can and usually will be different.

The width of the barrier areas obviously can vary. Due to theeffectiveness of the barrier areas these barrier pads do not need to beas wide as the reagent pads 13-15. This facilitates putting a largernumber of reagent pads onto a reagent test device since obviously thenumber of reagent pads can be varied from one up to 10 or more.Typically, reagent test devices measure 8×0.5 centimeters and whilethese dimensions can be varied the practical aspects involved inhandling and running several assays simultaneously dictates an upperlimit on the number of reagent pads which it is feasible or practical toincorporate onto a particular test device.

The material employed for the barrier pad can be the same as thatemployed for the reagent pads but normally is not. The barrier pad canbe impregnated with a suitable hydrophobic material including waxes,silicone materials and the like. Waxes which are especially useful inthe present invention are thermoplastic, water repellent, smooth intexture, nontoxic and have freedom from objectionable odor or color.Major types of waxes which can be employed include natural waxes, suchas animal wax, beeswax, spermaceti, lanolin, shellac wax; vegetablewaxes, such as carnauba, candelilla, bayberry, sugar cane; mineralwaxes, such as fossil or earth waxes, including ozocerite, ceresin,montan; and petroleum waxes, such as paraffin, microcrystalline,petrolatum; as well as synthetic waxes such as ethylenic polymers andpolyolether-esters including Carbowax, sorbitol and chlorinatednapthalenes such as Halowax and other hydrocarbon waxes. A preferred waxis the WW0404 wax from H. B. Fuller Company of Kalamazoo, Mich., whichhas the following characteristics: Melting point (ASTM D127) 82° C.±4%,hydrophobic, inert, bendable and not tacky when dry. The congeal point(ASTM D938) is 76° C.±4%, viscosity (Brookfield Thermocal) is 17.5 cps93° C., and color (ASTM D1500) is 1.0 Saybolt.

The important consideration in the present invention, regardless of whatmaterial is employed to impregnate the barrier pads from the barrier isthat the impregnation occurs prior to application of the barrier pad tosubstrate 12 such that impregnation occurs from all sides of the barriermaterial and this permits the barrier pad to be entirely impregnatedwith the hydrophobic material. One of the problems associated with priorart devices and especially with paper materials in which an attempt wasmade to create certain reagent areas and barrier areas in the samematerial by applying a coating or impregnating material to the surfaceof the material was that it was difficult to control and obtain a sharpline of demarcation between neighboring areas. Also it was difficult toassure that the material being impregnated was homogeneously impregnatedwith the desired impregnating material. Since the barrier pad isimpregnated completely before it is associated with the test devicesubstrate to form the ultimate test strip all of the barrier pad ishydrophobic.

In a preferred embodiment the barrier pad is formed from a hydrophobic,nonporous nonabsorbent material which is entirely different in characterfrom the hydrophilic material typically used to form the reagent matrixarea. Preferred materials include polystyrene, polyester,polyvinylfluoride and silica particles in an acrylic copolymer.

The width of the barrier pad 19 and 20 is not particularly critical, butthe presence of these pads tends to aid in preventing abrasion or damageto the reagent pads 13 and 15, respectfully.

From the foregoing, it will be seen that this invention is well adaptedto attain all of the ends and objects hereinabove set forth, togetherwith other advantages which are obvious and which are inherent to thesystem. For example, the present invention has the advantage ofconvenience, simplicity, relatively inexpensiveness, positiveness,effectiveness, durability, accuracy and directness of action. Theinvention substantially overcomes problems associated with runover whichhave been continuing and long felt with multiple reagent test devices.The reagent strip has minimum curvature since the reagent strip isstiffer and the minimum curvature provides better handling for bothvisual and instrumental readings. With all of the pads at a uniformheight the calibration of the system tends to be more reliable providinggreater resolution in the readings. Moreover, the test devices haveimproved appearance since there is no shadow at any side of reagent padand a clear color cutoff between the reagent pad and a barrier padprovides a strip with excellent appearance. A very important feature ofthe present invention is the minimization of damage to the reagent padsduring storage, transportation and use since the barrier pads tend toprotect the reagent pads. The uniform height of all the pads alsofacilitates improved visual readout by permitting the application ofsuitable background or negative colors as well as symbols on the barrierpads to facilitate reading of the reagent pads.

Obviously, many other modifications and variations of the invention ashereinbefore set forth can be made without departing from the spirit andscope thereof.

What is claimed is:
 1. The process of forming a reagent test devicecomprising multiple reagent carrier matrices attached to a substratewith hydrophobic barrier pads of identical height to the reagent carriermatrices in physical contact with and separating adjoining spacedreagent carrier matrices, which comprises bending the substrate materialfrom an original noncurved position so as to form a convex surface andthen applying the reagent carrier matrices and hydrophobic barrier padsadjacent to each other on the convex surface of the substrate andthereafter permitting the substrate to return to its original noncurvedposition to obtain a test device having reagent carrier matrices andbarrier pads of identical height in physical contact with each other tothereby protect the reagent carrier matrices from abrasion and toprevent liquid runover between adjoining spaced reagent carriermatrices.